1. Field of the Invention
The present invention relates to a method for the production of glass components, a redrawing apparatus for conducting such a method as well as a glass component.
2. Description of Related Art
In principle, the redrawing of glasses is known, in particular a comprehensive state of the art about the redrawing of blanks and/or blanks with circular cross-section for the drawing of glass fibers exists.
During a redrawing method a glass piece is partially heated and drawn in the longitudinal direction with the help of suitable mechanical equipment. When the glass piece—the blank—is fed into a heating zone at a constant speed and when the heated glass is drawn with a constant speed, then this results in a reduction of the cross-section shape of the blank which depends on the ratio of the speeds. So, when for example tubular blanks are used, then again tubular products are prepared, but with smaller diameter. The cross-section shape of the products is similar to that of the blank, wherein for the most part it is even desirable to achieve a reproduction of the blank in a reduced scale of 1:1 by suitable measures (see EP 0 819 655 B1).
In a step of redrawing glasses normally an oblong blank is fixed on one end in a holder and heated at the other end in for example a muffle kiln. Once the glass has become deformable, it is drawn by the exertion of drawing force at the end of the blank being fixed in the holder. When during the process the blank is moved forward into the muffle, then with a suitable selection of the temperatures this results in a product with a smaller cross-section, but a similar geometry. For example, a blank with circular cross-section is drawn into a glass fiber. The selection of the speeds of drawing the product of for example a component and optionally moving forward the blank determines the reduction factor of the cross-section. Normally, the ratio of thickness to width of the cross-section of the blank remains constant. In the case of drawing glass fibers this is desired, because starting from a blank with circular cross-section a glass fiber having also a circular cross-section can be drawn.
It has been proven that it is difficult to redraw flat components, i.e. components having a ratio of width to thickness of the cross-section of for example 80:1. Only with blanks having a very high width it is possible to draw components with also a high width. So e.g. from a blank having a cross-section of 70 mm width and 10 mm thickness (B/D =7) a component having a cross-section of 7 mm width and 1 mm thickness (b/d =7) can be produced.
A component having a cross-section with a higher width and the same thickness is only possible, when a blank having a cross-section with a higher width or lower thickness is used. The use of a blank having a higher width often fails due to the impossible producibility, and the use of a blank having a lower thickness is increasingly inefficient, since the blank during redrawing has to be exchanged more often.
In U.S. Pat. No. 7,231,786 B2 is described, how plane glass panes can be produced by redrawing. For achieving a product with higher width, in this case grippers are used which draw the soft glass into the width direction, prior to expanding the glass into the longitudinal direction with the help of edge rollers.
In U.S. Pat. No. 3,635,687 A a redrawing method is described, in which by cooling of the edge region of the flat blank a change of the ratio of width to thickness (B/D) is achieved. But with this method a maximum increase of the ratio of width to thickness by a factor of 10.7 can be achieved.
In EP 0 819 655 B1 a method for forming glass is described. In this case in the forming step also redrawing can be used. But it is not described, how the ratio of width to thickness (B/D) is adjusted. Here after heating the glass is locally heated or cooled for manipulating the geometry.
However, the manipulations described in these references only result in a smaller change of the geometry of the blank in comparison to the final shape and/or to the shape of the drawn component. Furthermore, these methods are associated with relatively high effort. In particular in the case, when grippers or rolls should be used, a sophisticated redrawing apparatus is required which is susceptible to defects.